(A and B) Effect of PF-4 on FGF-2 dimerization. Five nanograms ¹²⁵I–FGF-2 and 500 ng unlabeled FGF-2 were incubated in 45 μL PBS with or without heparin and specified PF-4 concentration. After 1 hour of incubation, 5 μL cross-linking reagent was added and the samples were incubated for further 30 minutes. At the end of the incubation period, extraction buffer was added and the samples were boiled and loaded on a 12% SDS-PAGE. The dried gels were analyzed by autoradiography. (A) Effect of increasing heparin concentrations (ng) on FGF-2 dimer formation in the presence of 1 μg PF-4. (B) Concentration dependency of the effect of PF-4 (μg) on FGF-2 dimerization in the absence (left panel) or presence (right panel) of 50 ng heparin.